Transcript Main Idea: Types of Volcanoes

Prepared by
Srusti Abinash Puri
&
Umakanta , Class VII
Guided by
Mr. Deepak Kumar
TGT(S.St)
What is Volcano?
Fissure or vent through which molten
rock material, or magma, and gases
from the interior of the Earth erupt on
to its surface, and the landform which
is produced as a result of this eruption
is known as volcano.
A. Structure of volcano
1. Volcanoes contain a
vent, crater and
slopes.
2. A vent is an opening
in the crusts surface
in which lava is
emitted.
3. A crater is connected
to the magma
chamber that is
located near the
vent.
B. What is a caldera?
1. A caldera is
sometimes
confused with a
crater.
2. They differ in size.
3. A caldera is
around 50 km in
diameter, while a
crater is at most 1
km in diameter.
C. How is a caldera formed?
1. A caldera is
formed when the
slopes of a
volcano collapse.
2. The top of the
magma chamber
becomes empty
from lava flow.
3. The caldera then
fills up with water
forming a lake.
Main Idea: Types of
Volcanoes
A. How does a Shield volcano
form?
1.
2.
3.
They form when
layers of lava
accumulate over
time.
The eruptions are
slow and
nonexplosive.
Shield volcanoes
are the largest in
size.
B. How does a Cinder-Cone
volcano form?
1. They form when lava
is ejected high into
the air and piles up
around the vent.
2. Small in size less
than 500 m high.
3. More explosive than
shield volcanoes,
because magma
contains more water
and silica.
4. Magma is more
viscous, which leads
to more gas
C. How do Composite-Cone
volcanoes form?
1. These volcanoes
form when layers of
lava alternate with
layers of volcanic
fragments (ash,
tephra).
2. Larger than cindercone
3. Are the most
dangerous of all
volcanoes
D. Where on earth can volcanoes
be found?
1.
2.
3.
4.
Volcanoes are found along plate boundaries.
80 % on convergent boundaries
15 % on divergent boundaries
5 % occur away from plate boundaries
E. Hot spots
1.
2.
3.
Areas on Earth’s
mantle where high
temperature causes
sections of earth to
rise (Hawaii).
The heat melts the
rock, which is forced
to the surface as
magma.
The magma melts
the crust forming
volcanoes.